Selective tuning system



May 28, 1945 G. s. wAcHTMAN 2,400,898

srnmzcTIvE TUNING `SYSTEM original Fiied oct. 5, 1943 con/MOL jo o V BY ja- @A/Mf J2 I C y AfroR/vfr Patented May 28, 1946 UNIT ED STATES Y PATENT OFF ICE 2,400,898 v SELECTIY-E TUNING :SYSTEM George S. Wachtman, Harrisburg, Pa. "Original application-ctobery5, :1943, SeralNo.

4505,048.` Divided and this vapplication Novembei-14, 1944, Serial No. 563,385 (c1. 25o- 40)` VMy invention relates Vbroadly .to Acircuit earrangements for high .frequency oscillators and more Aparticularly .to .a `circuit for .controlli-ng the resonant frequency `of tunable .circuits Vover a variable frequency `range with la high degree of precision.

This .application `is a division of my applica- .tion-.Serial `Number 505,048 for Electron -tube apparatus, filed October .5, .19.43.

One of the .objects .of my linver-iticn is to provide an improved circuit arrangement for controlling the resonant frequency .of electrically tunable circuits with 4a Ahigh degree of precision.

Another object of my invention is to provide a dual condenser controlled variable frequency oscillator circuit including a series connected adjustable means for compensating for the effectiveness of the respective portions of the dual condenser at any point in the frequency range of the oscillator circuit.

Other and further objects of my invention reside in the improved circuit ,arrangement for electrical tuning systems as set forth in the following specification and shown in the accompanying drawing in which:

Figure l diagrammatically shows the circuit of my invention; Fig, 2 shows a curve diagram showing the ideal characteristic curves of the cir-- cuit arrangement of my invention; and Fig. 3 illustrates practical conditions which may be encountered unless high precision operation is secured in the frequency control system of my invention.

Referring to the drawing which diagrammatically shows the oscillator system of my invention, reference character I designates the broad tuning condenser and reference character 2 shows the ne tuning dual condenser connected with impedance 3 as shown. The dual condenser 2 comprises a pair of xed stator sections 2a and 2b and a central rotor 2c and constitutes a splitstator or dual section variable condenser having capacities which vary simultaneously in the same direction. Reference characters 5 and 1 designate the trimmer condensers, whereby the control action of the fine timing dual condenser 2 may be adjusted and reference character 8 designates a condenser whereby the minimum or lowest tunable frequency of the combination may be adjusted.

A variable capacity condenser shown at 46 is connected in series between the rotor 2c of the dual condenser 2 and the impedance device 3. The variable condenser 46 is provided with a pad or trimmer condenser 4l in parallel therewith for increasing the jprecision adjustment of the .circuit. Condenser 41 is set Lor Aadjusted so that condenser -46 has that variation in capacity required =for compensating for the lack of linearity indual .condenser 2 as shown in characteristic curve .C' :in Fig. V3.

.'Due tothe fact that the two sections 20L-and 2b of the -dual Vvcondenser 2 always exert some control overthe resonant frequency of the circuit regardless of the setting of the main tuning control l, the ideal control characteristic for each .section .of .the :dual condenser is illustrated b y .curves A and B and .resultant curve C shown in Fig. 2 plotted with respect to total bandspread as ordinates and the tuning range of the main tuning control as abscissor. In practical operation it is realized -that such theoretically perfect operation may vnot be achieved.

Instead curves A and B' of Fig. 3 are actually obtained for the characteristics of the circuit of Fig. 1, the curve C being the resultant. Consequently, the means of compensating for the nonlinearity of curve C', Fig. 3, as provided in the circuit of Fig. l are important where accurate frequency controlled work is to be performed with the circuit. This is accomplished by the variable condenser 46 and the coacting pad or trimmer condenser 41 in parallel therewith operating in combination with the dual condenser 2. The action of the compensating condensers 46 and 41 is to adjust the minimum and maximum capacity of the parallel combination, thereby effectively controlling the tuning range of the bandspread control.

The circuit arrangement of my invention may be utilized for many purposes. The oscillator circuit may be connected to an oscillation system employed to test lapped quartz blanks for activity and frequency to a close tolerance before they are hand finished and put in holders. The circuit can also be used in receivers where it is desired to have a continuous bandspread of frequency; i. e., one that is constant at any setting of the main tuning control. In conjunction with a local piezo-oscillator (frequencyto be determined by type of use) and a receiver, and used in a stable variable frequency generator circuit by standardizing at time of use, the circuit can be used to determine the frequency of another signal within a few cycles. This is done by heterodyning the signal emitted by the generator against the unknown signal and detecting the heterodyne beat by audible or electrical or electro-mechanical means and then reading frequency by interpolation from a known standard signal (local piezo-oscillator) and the calibration on the dial of the ne-tuning control. The circuit can also be used to control the frequency of the emitted radiation of a radio transmitter, allowing the frequency to be varied over a wide range, and yet, by means of the fine-tuning control and prestandardization against a local piezo-oscillator or other Aprimary or secondary frequency standard, control the frequency within a few cyclesv of the desired frequency.

The applications of this invention, a's can be seen from the foregoing, are almost limitless.

The control circuit can be applied to any device kwherein the resonant frequency is desired to be variable. It can be applied to capacity-inductance or capacity-resistance or other impedance tuned generators or oscillators, to tuned circuits,

such as radio frequency, intermediate frequency or audio frequency stages in amplifiers, receivers, filters, etc., or to other tuned circuits wherein any combination of capacity, inductance, resistance, or reactance is used.

Features of my invention disclosed but not claimed herein are setY forth in the parent appli'- cation Seriai No. 505,048, filed October 5, 1943, for Electron tube apparatus; and my co-pending divisional applications, Serial No. 563,383, filed November 14, 1944, for Tuning system; and Serial No. 563,384, filed November 14, 1944, for Electrical tuning system.

While I have described my invention in one of its preferred embodiments, I desire it to be understood that modifications may be made and of the appended claim.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

An electrical tuning system comprising in combination with an impedance device, a variable tuning condenser havingone side thereof connected with a point on said impedance device, a dual condenser including a central rotor and a pair of variably related capacity areas constituting apair of condenser sections whose capacities vary simultaneously in the same direction, one of the condenser sections of said pair being disposed in series with said variable tuning condenser and the other of the condenser sections of said pair Lbeing effectively connected in parallel with the said'variable tuning condenser and effectively in paralle1 with said impedance device, independently adjustable variable capacity means connected in series with each of the condenser sections of said dual condenser, and said central rotor being electrically connected in` series with a separate variable condenser and another point of said impedance device for adjustably compensating for the effectiveness of the respective condenser sections at any point in the frequency range of the tuning system, and an additional variable condenser connected in parallel with said last mentioned separate variable condenser to increase the precision with which the latter may be adjusted.

GEORGE S. WACHTMAN. 

